Gap junctions represent direct intercellular conduits between contacting cells that permit the passage of small molecules (>1 kDa) including ions, metabolic precursors, and second messengers. The observation of extensive intercellular coupling and large numbers of gap junctions in the central nervous system (CNS) suggests a syncytium-like organization of glial compartments. One CNS infectious disease in which nothing is known regarding its impact on glial gap junction communication (GJC) is parenchymal infection with pyogenic bacteria leading to the establishment of brain abscess. Recent studies have revealed that several proinflammatory mediators detected in developing brain abscesses and produced by S. aureus activated glia, including interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-a), and nitric oxide (NO) are capable of modulating GJC in astrocytes and microglia. Specifically, these molecules attenuate GJC in astrocytes whereas activated microglia become functionally coupled. We have coined this phenomenon a "syncytial switch" and propose that the inflammatory milieu that develops during the course of brain abscess may be important for remodeling the types of interactions between resident glia and that deviation from physiological coupling may impact the integrity of brain regions distant from the primary focus of infection. These changes may be dictated by regional variations in Cx expression within the abscess. The objective of the proposed work is to investigate the functional importance of IL-1, TNF-a, and NO in regulating the glial syncytial switch and the role of Cx43 in brain abscess pathogenesis. To address this objective the following Specific Aims will be addressed: (1), to evaluate the consequences of S. aureus and its cell wall product PGN on homocellular GJC in primary astrocytes and microglia and the signaling pathways responsible for the syncytial switch;(2), to establish the functional importance of the proinflammatory mediators IL-1, TNF-a, and NO on modulating glial GJC in response to S. aureus stimulation using primary glia from knockout (KO) mice;and (3), to investigate the role of proinflammatory mediators on connexin expression and the functional importance of Cx43 in disease pathogenesis in a mouse model of S. aureus-induced experimental brain abscess using genetic KO models. Due to the extensive gap junctional coupling of glial cell populations in the normal CNS, neuroinflammatory disruption of normal glial syncytial networks could contribute, in part, to some of the long-term effects observed in patients following brain abscess resolution including seizures and cognitive deficits. These experiments will provide meaningful insights into how proinflammatory mediators influence the extent of glial GJC in brain abscess.